1. Technical Field of the Invention
The present invention relates to a contra-rotating propeller unit, a method for assembly thereof, a method for transportation thereof, and a method for mounting thereof on a mother ship.
2. Description of the Related Art
A contra-rotating propeller is a propeller system in which the rotational energy output from a front propeller is recovered by a rear propeller which rotates in a direction opposite to the front propeller and changed into a propulsive force so that high propeller efficiency is obtained. Hereinafter, a marine propulsion device mounted with a contra-rotating propeller is referred to as a “contra-rotating propeller marine propulsion device.” The contra-rotating propeller marine propulsion device is disclosed in the following Patent Documents 1 and 2, for example.
As one of conventional examples of the contra-rotating propeller marine propulsion device, the “propulsion device of ship” disclosed in Patent Document 1 is shown in FIG. 1. In FIG. 1, a propulsion device 100 of a ship is adapted such that an inner shaft 102 and an outer shaft 101 are concentrically disposed, a rear propeller 104 is attached to the inner shaft 102, a front propeller 103 is attached to the outer shaft 101, the inner shaft 102 is rotationally driven by a main engine 105, such as a diesel engine, an electric motor or a gas turbine serving as a first driving unit, and the outer shaft 101 is rotationally driven by a main engine 106, such as a diesel engine, an electric motor or a gas turbine serving as a second driving unit. In addition, reference numeral 107 designates a driving shaft of the main engine 106, and reference numeral 108 designates a gear transmission unit.    Patent Document 1: Japanese Patent Application Laid-Open No. 2005-67436    Patent Document 2: Japanese Patent Application Laid-Open No. 7-33084
Conventionally, it is usual that the installation of the propulsion device to a mother ship is performed in a construction shipbuilding yard. However, a contra-rotating propeller has a complicated structure in respect of various points, such as a bearing structure, a lubrication structure, and a seal structure, compared to a uniaxial propeller in order to allow contra-rotating operation. For this reason, in a case where a contra-rotating propeller type propulsion device is installed in a mother ship, it is necessary to have full knowledge of the assembly know-how regarding the contra-rotating propeller in the construction shipbuilding yard, and the installation is difficult in a construction shipbuilding yard which is lacking in the assembly know-how regarding the contra-rotating propeller.